Did you cc the chambers, or are you just assuming that 350 heads have larger combustion chambers? What's your piston depth? What thickness head gasket are you using? You can calculate all this out to target your quench and compression, or you can just throw the parts together and hope. There are enough pitfalls and parts combos that hoping isn't realistic. If I get time today (it's cold outside, so it may very well happen) I'll throw a spreadsheet together and post it so people can check their combos before assembly.